Swabbing method for initiating gas lift



Patented De@ 17, wl@

orales FRANCIS W.- LAKE, Oli" l/VHITTXER, CALFORNll-L, ASSIGNLS TO UNION OIL COMPANY UA'LLFRNM, 0l LOS ANGEL'*S, CALFOEiYi, A CORPQRATION GF CALIFORNEA SVABEENGT FOR INTEATING @Atl LIFT application led July 18,

lfhis invention relates to the so-c-alled gas litt method of owing deep wells, particularly oil wells, and has been designated to overcome the excess hydrostatic head of oil 5 which ordinarily accumulates in such wells prior to starting gas lift and which ordinarily cannot be removed by direct application ot a reasonable gas pressure in attempting to initiate gas litt.

Gas litt, as now commonly practiced, consists in passin gas under pressure into a well containing a i ow tube, so that the gas passes around the lower end ot the flow tube in a stream and in its passage atomizes the oil as is 'fast as it is forced up to said tube end by the natural rock pressure in the well, the atomized oil being carried to the surface in the` gas stream. The gas may be introduced either through the flow tube or through the zo casing, the atomized oil being discharged from the other of the two; however, it is pre- ;terred usually to introduce the gas into the easing and discharge the oil from the ilow tube.

But, as above indicated, the initiation oit gas lift usually offers ditliculties, due to the tact that during a preceding period ot idleness a. relatively great hydrostatic head ot oil has accumulated in thb Well hole, which head so usually cannot be overcome by steady application ot a moderate pressure to one side of the4 Iilow tube. This condition arises for the reason that, as pressure is applied to one side of the tube to depress the oil level therein,the

` hydrostatic head increases in the other side,

and, while some of the oil is forced back into the formation (depending upon the viscosity of the oil, the friction of the formation, and the like) the ed'ective roclr pressure in the 40 vicinity of the well increases until it is sufficient to balance the increased hydrostatic head., Thus, upon any attempt to start gas litt by straight application of pressure to one side in order to torce overl the entire excess load of accumulated oil and uncover theI lower end ot the tube "lor passage el gas thereunder, the hydrostatic head increase until it reaches the maximum, that is, until it is equal to the entire height ol the 5@ flow tube, which height be as much as a 1927. Serial No. 206,676.

few thousand feet, rlhis head may be greater than the available pressure. Moreover, the pressure which would be high enough to start gas lift by such steady application, that is, a normal starting pressure, under these conditions, would be excessive lor all other purposes, since when rthe oil level is lowered and gas litt started, normal continuation ot gas litt may be 'and should be carried on with a much lower pressure, this being made possible by the much lower density of the gas-and-oil column in the tlow tube during normal gas lift as compared with the oil before gas lift. Thus, it is clear that it is not convenient or desirable to maintain said excessive pressure merely for the purpose of overcoming said hydrostatic head.

rl`he general object ot the present invention, therefore, is to overcome the hydrostatic head and depress the oil level approximately to the lower end of the flow tube by the application ot gas under a pressure less than that required to initiate gas litt by steady application to either the tube or the casing in the usual manner, and less than the hydrostatic head naturally existing in the well prior to gas litt initiation.

rllhe present invention resides in initiating gas lift by introducing a swab into a low tube to a point low enough to obtain a satisfactory load of oil and then withdrawing the swab from the tube while maintaining. the mairimum available pressure upon the casing. The withdrawal or the swab tends to reduce the pressure there beneath, whereby it is possible to cause the well to flow with the assistance of a gas pressure which is much less than suiiicient to overcome the head oit oil in the well when applied unassisted.

ln the accompanying drawing wherein the steps in the operation of the method are diagrainmatically illustrated; I

l indicates the level 'to which the body of oil has risen in a well" wherein the hydrostatic head is too great to be overcome by the available gas pressure;

2 represents the introduction of a swab into the lower portion oit the flow tube;

llig. 3 shows the withdrawal of the sT the flow tube simultaneously the application of pressure to tlie casing whereby the level of the oil-body is lowered; and

Fig. 4 indicates the oil level when the excess has been entirely expelled and normal gas lift as been instituted."

An ordinary well casing 10 is shown as receiving flow tube 12 which depends into a body of oil which has risen in the casing to the level 14. Gas under pressure is adapted to be applied to the casing from a compressor 15 by way of an inlet 16. Since this pressure is insufficient to 'overcome the hydrostatic head, a swab 18 is lowered into the lower end of tube 12 b means of a line 2O until the desired load a ove the swab is obtained. The gas under pressure from the compressor 15 is supplied to build up in the casing as high a pressure as possible and the swab 18 is then withdrawn rapidly from the How tube. The tendency of the withdrawal is to create a lower pressure beneathithe swab and to draw a column of loil up through the lower portion of the tube. This eii'ect is assisted by the gas pressure being applied upon the surface of the oil in the casing, with the result that in most instances the combined efect is sutcient to force over the oil column and llow out the accumulated oil body. 1f flow cannot be established in one operation, the Iswabbing may be repeated until the head of oil is suiliciently lowered. l/Vhen the combined effect of the'swabbing and gas pressure becomes suflicient to overcome the head, the flowl ordinarily starts with a rush and often forcibly expels the swabs from the flow tube, the accumulated oil body bein rapidly discharged whereby the oil level is brought down to the lower end of the tube as indicated in Fig. 4. The gas being introduced into the casing then passes beneath the end of aid flow tube and in its passage aerates oi' atomizes the oil as it flows into the well thereby initiating normal gas lift and maintaining the oil level at approximately the lower end of the tube. :To

f continue :gas lift a pressure lower than the starting pressure ordinarily will be employed.

Since a swab is a long stroke pump, the invention in its broadest aspect extends to the use of pumping in'connection with applied gas pressure for the purpose of starting a well. Moreover the employment of Aa true pump during application of pressure will often cause a well to flow, in which case the pump rod, valves andassociated mechanism are withdrawn from the pump barrel when flow becomes established.

'lhis method very frequently may be conveniently used for reducing statichead preparatory to gas litt initiation and is relatively easy and simple to perform. llt may be ernployed where eective pressure, when steadily applied, is not sucient to start .gas litt by reason et any one ont the following causes:

eff pressure due to the escape of ,f1-as inte @pen sands;

Loss of pressure due to leakage ofl gas from the casing;

Insufficient gas volume;

Pressure inadequate to overcome the static head of the accumulated oil. 7o

Usually swabbing will relieve the static head suiliciently to enable they effective pressure in conjunction with the'swabbingeiects to kickov'er the oil column and clear the well as above described.

Preferably, natural gas is employed, but air or other gas may be used. Also gas may beintroduced from an adjacent well if the pressure is suiiciently high, thereby eliminating the compressor.

As specic examples, a well which-would not start on straight application of 820 pounds on the casing, was swabbed with 725' pounds on the casing, and the well immediately began to ilow, gas lift being then continued with 200 pounds. Again Awhere 800 pounds was insuilcient on straight application, the well beg-an to llow with 300 pounds on the casing, and gas lift was continued thereafter-with 150 pounds.

It is to be understood that the above disclosures are considered merely as illustrative and not as4 limiting, since many variations of the invention may be made within the scope of the following claims. i

I claim: f

1. A method for initiating gas lift in wells containing a liquid head comprising simultaneously swabbing and applying to the liquid surface gas under pressure from an outside sturce.

2. A method for initiating gas lift in oil wells containing a liquid head comprising reducing the eective static head by swabbing and simultaneously applying to the liquid surface gas under pressure from an outsi'de source until flow is established.

3. A method for initiating gas liftin oil wells containing a liquid head which comprises reducing` the static head of oil in ,a well by swabbing to a point suliicient for the initiation of gas lift when gas at a predetermined pressure is applied to the oil surface from an outside source, and so applying gas at the predetermined pressure to the oil ils surface from the outside source.

4. A method for initiating gas lift in an oil well having a casing through which a flow tube depends into a body of oil in the casing, comprising introducing a swab into the tube, withdrawing the swab to remove a quantityl of oil and reduce the static head in the tube, and simultaneously applying gas from an outside source under lpressure to the surface of the oil in the casing to assist theV swabbing action and to start gas litt.

5. A method for initiating gas litt in an oil well having a casing in which a tube depends inte body et oil, comprising applying gas an source under prest3@ sure to the oil surface on the outside of the tube and simultaneously mechanically pump-y ing oil out through the tube with a reciprocating piston pumpl working upon the oil until gas lift is established.

5 6. A niethod for effecting gas lift in an oil Well having afcasing'in which a tube depends into a body of oil, comprising applying gas from an outside source under pressure 'to the oil surface on the outside of the tube and silo multaneously pumping oil outthrough the tube until gas liftis established and then discontinuing the pumping while maintaining the gas pressure to continue gas lift.

7; A method for effecting gas lift in an oil well having a casing in which a tube depends into an oil body, comprising applying gas from an outside source under pressure to the oil on the outside of the tube and simultaneously Withdrawin quantities of oil from the tube to reduce the ydrostatic head in the tube withoutadmitting gas to the tube, discontinuing the withdrawal of said quantities of oil when said gas enters the tube, and maintaining the gas pressure to initiate and continue the. flowing of the well by gas lift at said reduced head.

Signed at Los Angeles, in the county of Los Angeles and State vof California, this 12th 30 day of July, A. D.`1927.

FRANCIS W. LAKE. 

